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GENERATORS HELP and DESIGN. Click here ~> TABLE of CONTENTS to go to topics of interest.
This page is being written to simplify and explain generator choices, and benefits and options for automatic and manual transfer switches. Some information contained here will help in decisions of types and sizes of generators, and the best type of transfer switch for your application.
Note: If there are topics that are not covered here, writing a letter to the firstname.lastname@example.org would help us to know what items to add. Also, if requested, we may attempt to contact you and answer questions you have.
GENERATOR BASICS: Generators are mostly chosen for two features, to be portable or permanently mounted, and the type of fuel they run on. Fuel options are diesel, natural gas, propane, and gasoline. A portable generator will be mounted on wheels and is usually gasoline powered, and larger units are generally mounted outside on concrete pads. Some generators come pre attached to plastic pads.
WARNING: Generators fumes are dangerous and can be deadly. Generators produce fumes when running, and must be operated outside and away from exhaust flow into populated rooms.
About Portable Generators: The benefit of the portable generator units is that they don't have to stay on one location so they could stowed away when not in use and placed outside to operate. For temporary electrical, portable generators are usually better when used with extension cords and not connected to a transfer switch. While some can be large and run parts of an entire home, they can also be small and lightweight, but strong enough for a few lights and the refrigerator, or a portable heater. One suggestion mentioned that is also possible with a portable generator is to install a small window air conditioner temporarily when the power is expected to be out for some period of time.
Please note: The power outputs for a wheeled generator often do not give a single output source that equals the full rating of the generator. For example, a larger portable unit might be rated for 15,000 watts, which could supply up to 62.5 amps on 240 volts, but offers a 50 amp 240 volt receptacle and a 30 amp 240 volt receptacle and assorted 20 amp receptacles. Generally speaking, it is best to use portable generators with extension cords. Also note that other methods of wiring may not be supported by the warranty. Please read warranty and installation paperwork.
About Permanent Generators: The advantage of a portable generator is often the type of fuel to be used. The fuel tank can be mounted nearby or even below the generator when using diesel, and can be tied into the natural gas used inside the house when available. A transfer switch should be a part of the design for permanent generators. When used with an automatic transfer switch, the generator can be set on an automatic cycle to exercise the generator periodically, which should increase the reliability.
TRANSFER SWITCH OPTIONS:
There are two types of transfer switches, automatic and manual. Also, they can be either control the whole building, or they can be a sub panel with breakers inside, and connectted to the house breaker panel. Both of these options required some decisions before purchase.
If they are to control a whole house, they would usually mount outside, near either the generator or the meter base. If they are a sub panel type, they are most often mounted near the inside breaker panel.
With a transfer switch, there is no need to turn off the building main breaker. The transfer switch is doing that job for you by moving the power source away from the utility and to the generator. The transfer switch may be required by law in certain localities, and makes it safe for a lineman working on the power lines without the possibility of generator power traveling up to the power lines.
WARNING: When power from a generator is able to travel back up to the power supply, the 240 volts in the home is then transferred back into the same high voltage usually supplied by the power company, creating a potentially deadly hazard for linemen working on restoring power. Do not use any system that does not have complete separation between the generator and the utility power. Transfer switches eliminate that hazard.
Two options for transfer switches: automatic or manual.
NOTE: Transfer switch installations are not an item to be done by a homeowner. The method of tying in the generator power into the building electrical, and the requirements for grounding are all items that should be done by a licensed electrician.
Auto transfer switch benefits: The sequence of events for an automatic transfer switch will be to: automatically detect when you lose utility power, signal the generator to start up, then switch your power from the utility company to the generator. Once your power comes back on, it will switch back to the utility company power, and then cool the generator down by running it with no power load before shutting it off. The start up and transfer time can be expected to be between 10 and 20 seconds if the battery is good and the generator is kept in good working condition. This series of events does not require anything by the owner, except to assure that enough fuel is available, and a battery in good working condition.
Manual transfer switch benefits: Primary benefit is about the cost. The sequence of events are: you start the generator, then manually change the transfer switch power from utility power to the generator, usually by moving a lever in the transfer switch. When the power is restored, you go back to the transfer switch to switch back to utility power, and maybe run the generator a few minutes to cool it off before shutting it down. The generator must be kept in good running condition to insure reliable start-up when needed.
The two main differences between the manual and the automatic transfer switch are that the generator is started and stopped manually, and regular running of the generator should also be done. A manual transfer switch will require going out into the elements to start and stop the generator.
Two more options for transfer switches: Whole house or sub panel transfer switches?
Generators are often sold along with the transfer switches, as in a package deal. They can be transfer switches that are small panels with the electronics inside, and a limited number of breakers, the sub panel type, or they can be larger boxes that mount outside and control the whole building instead. The following is some detail that may help in making the decision for sub panels vs. whole house transfer switches.
About Whole House Transfer Switches: Transfer switches that control the whole house will be boxes usually installed by the meter or near the generator. They are usually larger than the sub panel type, and must carry the same amperage rating as the panel they supply power to, although the generator itself can be much smaller. The transfer switch carries all the power of the panel during normal use.
Using less power on a generator saves fuel. Since the full power output would normally be less than the full power rating of the building, there is a limit to how many different items can be running at a time. A generator that is large enough to run the air conditioner or heater, a sump pump if there is a basement, plus some lights, a television and maybe a few more small items might be more than sufficient if the power might be off for an extended period. Since there will not be a full amount of power available, different items can be selected to run at different times. For instance, if the heater or air conditioner can be turned off, that would allow the power available to run the cook top. The important advantage of a whole house transfer switch is that there is not a limit to what can be operated, but instead, how much can be operated at any given time. Also read the section on Sub Panel Transfer Switches.
About Sub Panel Transfer Switches: Generators can be sold as a package including the transfer switch. Sometimes this will be a sub panel type transfer switch, which might also have the benefit of being an automatic transfer switch. A sub panel is a panel that is mounted near your breaker panel, and includes a limited number of breakers inside it. It is connected to the breaker panel with a flexible conduit. It will have normal power supplied from the electrical panel, and when there is a power outage, the generator supplies power to the sub panel. The rest of the house is not powered. The breakers that are in the sub panel are selected to be the ones that would have power during the outage.
To install this sub panel, the breakers inside the sub panel are matched to breakers inside the existing breaker panel. Breakers that supply power to parts of the house you want powered during a power outage are chosen to be wiring into the sub panel. Since there is a limited amount of breakers available, it is important to make sure that this will supply everything critical during the outage. In choosing the items to be powered, be sure to consider the heat or air conditioner, and the sump pump if required, among other items. There are limitations to this type of transfer switch. Also read the section on Whole House Transfer Switches,
When there are two disconnects,
When gasoline is stored for an extended period of time, it breaks down and damages the fuel system of a generator. There are two possible solutions .
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Generators create noise when operating. Placing a generator
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